and agents keith carpenter and tim bean. >> anytime you have an al qaeda in iraq operative in the u.s. >> reporter: at the prompting of an fbi informant who befriended the men, alwan made these drawings of i.e.d.s he said he made back in iraq. and in undercover tapes of the informant he boasted of building a dozen or more bombs and using a sniper's rifle to kill american soldiers in the baji area. >> he said he had them for lunch and dinner. meaning he had killed them. >> to hear him say that on the undercover tapes must have been chilling. >> it was gut-wrenching. >> reporter: but the big breakthrough in the case came out of this warehouse outside washington. an fbi repository of virtually every ied or bomb used against american targets anywhere in the world. >> this is basically america's bomb library. >> reporter: the remnants of some 100,000 bombs are stored in these boxes, stacked to the ceiling here, as part of a little-known fbi unit run by gregory carl. >> when you really stop and think about what's actually in those boxes is really what makes you pause, thinking of all the tr